This invention relates to novel chemical compounds structurally related to phosphatidylcholine, to a method of preparing such compounds, and to the use as surfactants of such chemical compounds with or for compounds which have limited or no solubility in aqueous solutions.
Phospholipids and phosphatidylcholine in particular are amipathic compounds in that they consist of a hydrophobic and hydrophilic group or region within the same molecule. Compounds with this amipathic property tend to self-associate in aqueous systems to form micelles which have a hydrophobic interior and a hydrophilic exterior. As a result, these compounds act as surfactants and can solubilize other relatively aqueous insoluble compounds which have limited or no solubility in water, and can partition such insoluble compounds into the hydrophobic region of the micelle. The external polar hydrophilic region of the micelle confers water solubility on the micelle complex or group. It has been well known that such nonsoluble biological compounds, such as cholesterol, cholesterol esters and derivatives, triglycerides and other compounds, can be solubilized in phospholipid micelles. However, the extent of solubilizing power of any surfactant is highly dependent on the ratio of hydrophobic-to-hydrophilic balance within the particular molecule.
For example, natural phosphatidylcholine (that is, lecithin) is an excellent emulsifying agent for a number of insoluble biological compounds, such as cholesterol, cholesterol esters and triglycerides, and lecithin is widely used in many industrial applications; for example, the food industry. Lecithin is a natural surfactant, and, like other such surfactants, its solubilization properties are derived from its amipathic character; that is, the molecule possesses a region of hydrophobic character (the heterogeneous fatty-acid chain) and a region of hydrophilic character (the polar head group - ethyl-n-trimethyl group). In addition, lecithin is zwitterionic in the pH range of 2-12, because it possesses a positively charged group (the quarternary ammonium group) and a negatively charged group (the phosphate group). This zwitterionic character stabilizes the ionic structure of the lecithin against any pH fluctuations that would tend to flocculate other natural detergents; that is, other phospholipids or bile salts.
The natural occurring phospholipids are limited in solubilizing properties. For example, it is known that the maximum amount of cholesterol that phosphatidylcholine can solubilize is in a molar ratio of about one to one, while little, if any, cholesterol ester can be solubilized by phosphatidylcholine. Thus, novel phospholipid compounds which have modified solubilized properties (particularly those which solubilize a greater amount of both biological and industrial compounds than is possible with the natural compound or have different solubilized properties) would be most desirable and useful.